The ankle is one of the most frequently sprained joints in the body. The most common and often most severe ankle sprains are caused by excessive inversion or eversion. Inversion is the internal rotation of the ankle joint. Eversion is the external rotation of the ankle joint. The occurrence of injury to the ankle can be significantly reduced by limiting inversion and eversion. This can be accomplished by restricting medial and lateral motion of the ankle.
When restricting ankle motion, it is important not to hinder the natural plantar and dorsi motions of the foot and ankle, as this will lead to decreased performance during athletic activities. Plantar flexion is a toe-down motion of the foot at the ankle, and dorsi flexion is a toe-up motion of the foot at the ankle. The axis of motion for plantar and dorsi flexion must be considered when limiting any ankle motion.
Prior art devices and methods for minimizing the risk of a sprain include taping the ankle to immobilize it against excessive rotation and building support systems into articles of footwear. Taping the ankle of an athlete is a time consuming and expensive procedure which generally cannot be performed by the athlete. Rather, it requires a trainer with special knowledge of how to properly and effectively tape an ankle in order to protect it from being sprained. Taping an ankle can severely limit its natural plantar and dorsi flexion.
Prior art articles of footwear have attempted to deal with ankle injuries by incorporating support systems which limit ankle motion. These systems do not provide sufficient protection against inversion and eversion while allowing essentially unrestricted dorsi and plantar flexion. Instead, they use rigid members, elastic materials or straps which unnecessarily add to the overall weight of the article of footwear, make the article of footwear more cumbersome and uncomfortable and restrict plantar/dorsi flexion. An example of such a system is U.S. Pat. No. 2,634,515 to Saitta which discloses a spiked article of footwear having a plurality of stiffeners in the form of flat steel ribs located in pockets along the sides of the article of footwear for preventing eversion and inversion. The steel ribs significantly increase the overall weight of the article of footwear while impeding flexion in the dorsi and plantar flexion directions.
Recent attempts to incorporate ankle support systems into athletic footwear have resulted in footwear which insufficiently prevents inversion and eversion and/or significantly impedes dorsi/plantar flexion. U.S. Pat. No. 5,152,082 to Culpepper discloses an ankle support member formed from a stiff, resilient piece of bendable sheet material. The support member includes a base having a plurality of medial and lateral strips extending upwardly and rearwardly therefrom in the direction of the heel. The width of each strip is significantly greater than the distance it extends away from the interior wall of the article of footwear. Accordingly, each strip has great strength for resisting flexion in the plantar/dorsi flexion plane and little strength for resisting flexion in the medial/lateral plane. As a result, these strips prevent adequate flexion in the plantar and dorsi flexion plane while allowing inversion and eversion.
U.S. Pat. No. 4,989,350 to Bunch et al. discloses a high top article of footwear having sheet springs rigidly fixed to the upper of the article of footwear at points below the wearer's ankle. The springs are not affixed to the upper above the wearer's ankle so they do not move with the flexion of the article of footwear to fully support the ankle and foot no matter their positions. Further, the struts are designed so that they extend a distance along the length of the article of footwear which is greater than the distance they extend away from the article of footwear. As a result, the struts resist plantar/dorsi flexion more than they resist inversion and eversion.
U.S. Pat. No. 5,498,033 to Hoshizaki et al. discloses a hockey skate having a skate boot with a molded plastic overlay for restricting movement of the wearer's ankle. The overlay increases the rigidity of the rear of the skate to restrict medial and lateral movement of the ankle. The material of the overlay also resists dorsi and plantar flexion.
There is a decided need in the art for an article of footwear which limits inversion and eversion while providing the needed amount of flexibility in the plantar/dorsi flexion plane. There is also a decided need in the art for a support which is comfortable and conforms to the contour of the ankle and foot of a user.
It is an object of this invention to overcome the disadvantages of the prior art by providing a lightweight article of footwear having the optimum amount of flexibility, support and comfort.